Genetic diversity of Echinacea species and the regulatory role of PAL in caffeic acid derivative accumulation
Abstract
Echinacea products have gained considerable attention in the botanical and nutraceutical markets as general immune system enhancers in the rapidly growing field of dietary supplements. Among Echinacea species, the natural products suspected of contributing to the biological activity of the genus are several caffeic acid derivatives (CADS), which are also strong antioxidants, and one of which, cichoric acid, possesses potent anti-HIV activity. A great deal of research focused on the phytochemical characterization and pharmacological activity of Echinacea has been conducted; however, little information is available regarding the genetic diversity present in germplasm of Echinacea species useful for their improvement with respect to phytochemical profiles, nor has the biochemistry and regulation of natural product accumulation in the Echinacea been characterized. This research represents a foundational effort to address these issues, beginning with the characterization of the genetic diversity of germplasm of the three commercially utilized species using random amplified polymorphic DNA (RAPD) markers and quantitative analysis of CADs, which permitted the identification of sources of potentially unique genetic material. The accumulation of CADs was also characterized relative to the activity of phenylalanine ammonia-lyase (PAL), the first step of the phenylpropanoid biosynthetic pathway, which is regarded as a key control point for this pathway. Analysis of PAL activity and CAD accumulation in young plants of three commercially utilized species, as well as an elicited plant system and a tissue culture system with exogenous substrate provision for E. purpurea, revealed that other factors contribute to the regulation of CAD accumulation. Total caffeoyl moiety accumulation correlated with PAL activity for root tissue across species, while no correlation was seen for shoot tissue. E. purpurea exhibited the highest PAL activities and CAD accumulation in general. Elicitation resulted in substantial inductions of PAL activity without a corresponding increase in CAD production. Exogenously supplied phenylalanine suppressed PAL activity in tissue culture explants, but was rapidly incorporated into CADs and stimulated increased accumulation of chlorogenic acid but not caftaric or cichoric (caffeoyl tartaric acids). A genetic transformation system for E. purpurea was also established to permit a biotechnological approach to investigation and improvement of natural product accumulation in this species.
Degree
Ph.D.
Advisors
Simon, Purdue University.
Subject Area
Molecular biology|Botany
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